1. Field of the Invention
This invention relates to a channel selecting apparatus to be used for CATV receivers and television receivers.
2. Description of the Related Art
Generally, the CATV is multi-channeled to diversify the television service. For example, in the United States of America, a multi-channel CATV system realizing the transmission exceeding 100 channels is operated and a channel selecting system including a tuner so that the receiver may also correspond to it is designed.
As a channel selecting operation system wherein the receiving channel is designated in a CATV receiver or television receiver, there is a system wherein the channel number is continuously sequentially switched. That is to say, the channel number is sequentially made to rise up to a larger number from a smaller number or to fall down reversely to a smaller number from a larger number to select a desired channel. This is called an up/down channel selecting system.
In this up/down channel selecting system, in order to elevate the operatability, the system is generally set to move to the next channel by skipping over a channel not broadcasting at the time of selecting the channel or a channel in which no receiving is desired. That is to say, it is preset to skip the channel. In a presetting method, the number of the channel desired to be selected is memorized in the address position corresponding to this channel number of a memory (RAM), a region in which the information as to whether this channel is skipped or not is written, that is, a skip flag is set and the skip information of each channel is memorized in the skip flag.
In a receiver wherein the same tuner is used so that both of a CATV and TV may be received, as shown in FIG. 20, for example, a total of 181 CH of 1 to 125 CH (CH is an abbreviation of the channel here and also hereinafter) of the CATV and 14 to 69 CH of the UHF of the TV are made to correspond to position numbers 1 to 181 and are provided respectively with skip flags. This example is based on the actual channels readily available in the United States of America, and 2 to 13 CH of the VHF of the TV and 2 to 13 CH of the CATV are of substantially the same frequency and the same positions.
As shown in FIG. 20, one bit is required for each of the skip flags corresponding to 181 CH and a memory capacity of 181 bits is required in order to realize the preset. Generally such channel selecting system is formed of a microcomputer but, there has been a problem that, as the capacity of the memory (RAM) is limited, if the above mentioned memory capacity (of 181 bits) is to be secured, it will have to be selected whether the function of the microcomputer is reduced or the memory is externally fitted. That is to say, there has been a problem that the memory (RAM) capacity of the conventional microcomputer is so small that the number of the skip flags can not be taken to be so large.